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bh=wWP43UEjIhSOrpWkPnDsO8fIdGTKQp3AyeDzseDGv1Y=; b=rBcgbjWPxK9kYA6qX1WnnzkvdYL+6qXWN/bZ62OAZMj0CeWPPAYsuQTvkhxJ1UjDiizJfs 9ZbqtWp5e9X/esVs2FfrwwKZhDqSKWrd4Dk32EWLXEzD9jdhao2bZOyGoVD6uSEOupLqbY oRfHeUO404V4Yf5Nml8jx2306jsERWU= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id B6C1F2C141; Mon, 3 Apr 2023 12:53:05 +0000 (UTC) Date: Mon, 3 Apr 2023 14:53:05 +0200 From: Petr Mladek To: Jaewon Kim Cc: "senozhatsky@chromium.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "jaewon31.kim@gmail.com" , GyeongHwan Hong Subject: Re: [RFC] vsprintf: compile error on %09pK Message-ID: References: <20230403104617epcms1p383bacbca705c0d7e4fffca6833050e42@epcms1p3> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230403104617epcms1p383bacbca705c0d7e4fffca6833050e42@epcms1p3> X-Rspam-User: X-Rspamd-Queue-Id: 529CF40013 X-Rspamd-Server: rspam01 X-Stat-Signature: 6rb39wo4yg459g7tordfd4pfgitit8nq X-HE-Tag: 1680526387-821703 X-HE-Meta: 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 DOvyPFfw mRcI0j2v31wH285Cr8ZuOKnXL41oyS8VS0dKT9eWSgL+hXlCyFiawHVih2NIBzBvWdioa28oQHS7UY0RLjGkbtkR3/xjhtgUrFxZbCazYzs53+q69rwgrh/QnsfsziPHVR9TOZ3+kXvy6lcVty1lVWwZLxx0RFB+6Ahss4szvAjznTXJt607U3wjxdmtXUhRZh117XszUy3TrHMA+wiKBUFHnUqPg/BJEHzwndPF10BeeNT+dKU/FICtJ5lVAdppp7dnuEHAELkcwd5aQX7jE/vyM2A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 2023-04-03 19:46:17, Jaewon Kim wrote: > Hello > > I've just changed %09lx to %09pK on my driver code to hide the address, but I > faced compiler error. The %9pK without 0 worked. What exactly do you want to achieve, please? Note that printk() hashes pointers by default. It means that %p does not print the value but a hash based on the value. If you print the same pointer twice, you will see the same hash, so you know that the pointer is the same. But you do not see the address so that you could not use the value for a security attack. See Documentation/core-api/printk-formats.rst Anyway, the main question if it makes sense to print the pointer value at all. The address is not useful if it can't be compared with other pointers or if the data on the address could not be checked. > Is there restriction on %pK which does now allow %0 ? I've wondered whether I > did wrong or it is a printk problem. > > To show easily I tried to add pr_info("%09pK\n", nodemask); in page_alloc.c > Then here's what I did. > > $ ARCH=x86 make x86_64_defconfig ; make mm/page_alloc.o > # > # No change to .config > # > CALL scripts/checksyscalls.sh > DESCEND objtool > INSTALL libsubcmd_headers > CC mm/page_alloc.o > In file included from ./include/asm-generic/bug.h:22:0, > from ./arch/x86/include/asm/bug.h:87, > from ./include/linux/bug.h:5, > from ./include/linux/mmdebug.h:5, > from ./include/linux/mm.h:6, > from mm/page_alloc.c:19: > mm/page_alloc.c: In function ‘__alloc_pages’: > ./include/linux/kern_levels.h:5:18: error: '0' flag used with ‘%p’ gnu_printf format [-Werror=format=] > #define KERN_SOH "\001" /* ASCII Start Of Header */ As Sergey already wrote. %p does not support any modification flags. Best Regards, Petr